On 2 September 2014 21:04, Eric Blake <ebl...@redhat.com> wrote:
> On 09/02/2014 04:24 AM, Peter Maydell wrote:
>> +
>> + if (host == NULL || strlen(host) == 0) {
>> + host = "localhost";
>> + }
>> + if (port == NULL || strlen(port) == 0) {
>> + error_setg(errp, "chardev: udp: remote port not specified");
>
> In the common case of these strings being non-empty, you end up having
> to hunt for the end of the string only to then throw that information
> away. Rather than 'strlen(foo) == 0)', it's slightly faster to check
> '*foo' for being a non-NUL byte.
I think that's a lot less clear to read, and in fact the
compiler is entirely capable of turning "strlen(x) == 0"
into "check whether *x is 0":
mnementh$ cat /tmp/zz9.c
#include <string.h>
int is_empty_string(const char *s)
{
return (strlen(s) == 0);
}
mnementh$ gcc -g -Wall -O2 -o /tmp/zz9.o -c /tmp/zz9.c
mnementh$ objdump --disassemble /tmp/zz9.o
/tmp/zz9.o: file format elf32-i386
Disassembly of section .text:
00000000 <is_empty_string>:
0: 8b 44 24 04 mov 0x4(%esp),%eax
4: 80 38 00 cmpb $0x0,(%eax)
7: 0f 94 c0 sete %al
a: 0f b6 c0 movzbl %al,%eax
d: c3 ret
thanks
-- PMM
